The multiple inert gas elimination technique (MIGET) is an established research tool for the determination of ventilation/perfusion (V/Q) distributions in the lung, and the pathophysiologic mechanisms of impaired gas exchange. The MIGET would be tremendously useful for optimizing therapy in the clinical care of patients with pulmonary dysfunction. The traditional approach to MIGET by gas chromatography, however, is laborious and time consuming and as a result has only been used by a handful of research laboratories throughout the world. In phase I of this project, we applied recent developments in membrane inlet mass spectrometry (MIMS) to the measurement of V/Q distributions by MIGET. We established that MIGET by micropore MIMS is far superior to traditional MIGET, with radical reductions in blood sample volume and in analysis time. In phase II of this project, we will optimize the design of the current proof-of-principle inlet system and automated sample handling system. We will design, construct, and test a custom purpose mass spectrometer that is suitable for low-cost mass production. We will assemble and rigorously test first- and second-generation prototypes of a complete, automated, commercial system for MIGET. The resulting commercially marketable system for MIGET will extend this important research tool to the clinical care of patients. PROPOSED COMMERCIAL APPLICATIONS: V/Q distributions determined by a rapid and automated MIMS method will be useful for diagnosis, for suggesting therapeutic strategies, and for monitoring the response to therapy in patients with pulmonary dysfunction, particularly critically ill patients. The market for MIGET by MIMS includes virtually every intensive care unit in the world.